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Cell types Sclereids Sclereids are specialized cells formed in a variety of shapes. Pits They have lignified secondary cell walls and are non-living at maturity. Ramified pits Their primary function is for mechanical support and protection. Lumen Side wall pits and a central lumen are common features of sclereids. Sclereids in pear fruit Back to main anatomy menu Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids Sclereids come in a diversity of shapes and can be found in leaves, petioles, stems, fruits and seeds. Sclereid in a Camellia leaf with prominent central lumen and radiating pits. Back to main anatomy menu Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids The diversity of sclereid shapes makes a definitive classification system difficult. Several distinctive sclereid types include: Brachysclereids Macrosclereids Osteosclereids Astrosclereids Trichosclereids Filiform sclereids Back to main anatomy menu Back Colorized electron micrograph of macrosclereids in Geranium seed coat. Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids Brachysclereids have an isodiametric shape that resembles parenchyma cells, but they have a thick secondary cell wall. These non-living cells are also called stone cells. Brachysclereids in purple coneflower seed (achene) Back to main anatomy menu Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids Brachysclereids are common in cortex of stems and fleshy tissue of some fruits. The “grit” found in pear fruits are brachysclereids. Brachysclereids (stone cells) in pear (Pyrus) Back to main anatomy menu Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids Macrosclereids are elongated sclereids usually found in the outer layer in the seed coat of seeds (especially legumes). Macrosclereids These cells are responsible for restricting water uptake by seeds with physical dormancy. They are also called Malphigian cells after the pioneering Italian 17th century plant anatomist. Seed coat in eastern redbud (Cercis). Back to main anatomy menu Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids These macrosclereids cells in a developing bean (Phaseolus) seed coat are densely packed together. They elongate to their full length prior to secondary wall formation. Macrosclereids Lumen Isolated mature macrosclereid cells show thick secondary wall formation and central lumen. Back to main anatomy menu Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids Bur cucumber (Sycios) produces a central lumen that is branched towards the ends of the macrosclereid. Lumen Secondary cell wall Macrosclereids Back to main anatomy menu Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids The light line is a continuous line just beneath the outer surface of the macrosclereids in some seed coats. Light line Macrosclereids It is actually, an optical refraction of light due to the physical properties of the macrosclereid. It was once thought to be responsible for making these cells impermeable to water, but this is probably not the case. Back to main anatomy menu Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids This colorized electron micrograph of the seed coat in Geranium shows the light line and the waxy covering on the tops of the macrosclereids. Macrosclereids Light line Back to main anatomy menu Waxy cuticle Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids Osteosclereids (also called bone or hour-glass cells) are columnar cells found in legume seed coats. They have a similar protective function as macrosclereids. They are enlarged at the ends making them bone-shaped. Macrosclereids Osteosclereids Macerated pea (Pisum) seed coat Back to main anatomy menu Back Next Seed coat in yellowwood (Cladrastis) Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids Astrosclereids are branched, pointed, irregular (often star - shaped) sclereids. Astrosclereids are not a common type of sclereid. They can be found in specialized tissues like the floating leaves of water lily. Back to main anatomy menu Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids Trichosclereids are also branched sclereids with arms that project into intercellular spaces. The same sclereids described as astrosclereids in water lily are also identified as trichosclereids because of this intercellular growth habit. Waterlily (Nymphaea) leaf cross-section Back to main anatomy menu Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids Branched trichosclereids growing between the palisade cells of the leaves in Osmanthus. Back to main anatomy menu Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids The sclereids in Camellia also grow between leaf cells but may not be branched. Back to main anatomy menu Back Next Sclerenchyma menu Back to cell types menu Main menu Cell types Sclereids The long thread-like sclereids in the aerial roots of the Swiss cheese plant (Monstera sp.) are probably best described as filiform sclereids. Back to main anatomy menu Back Sclerenchyma menu Back to cell types menu Main menu
